Is there a way to make a custom Page type?

In a theme I’m building, there are two main types of page. One is a product-gallery, one is for general info. I’d like to use wp_get_pages() or wp_list_pages() twice in the sidebar, one with a list of one type of page, and one with the other.

I don’t want to hard-code include or exclude in either list, as I can’t predict which page IDs will be which type of page. So I’d like to do something like:

wp_list_pages(‘type=gallery’)

and

wp_list_pages(‘type=page’)

What technique should I be using here?